Satisfactory progress is being made on the synthesis of the C-nucleoside analogs of 5-fluorouridine and 5-fluoro-2'-deoxyuridine. The synthesis has almost been completed of the acetylenic "suicide" inhibitors of de novo pyrimidine biosynthesis, 5-ethynyl-5,6-dihydrouracil and 5-ethynyl-5,6-dihydroorotic acid. Five new 1,2,4-triazin-3-one-1-oxides, as well as 6-methyluricytin, have been synthesized as potential chemoimmunotherapeutic agents. A comparative study of the modes of action of uricytin and showdomycin was conducted. The deoxyribonucleoside of 3-deazaguanine was synthesized, as well as the corresponding N-7 isomer.